This invention relates to a navigation apparatus for guiding a driver to his destination by selecting a course leading to the place input as the destination while calculating the present position at every intersection along the way to the destination.
Navigation apparatus are known as an apparatus used to guide a driver who is a stranger in a certain region to his destination in this region by selecting a suitable course leading thereto. Apparatus of this kind are now developed eagerly.
In a conventional navigation apparatus, a course along which a driver will be led to his destination is set on the basis of a starting point and a destination point input before the driver starts traveling. The driver navigates along the course thereby set. There are various methods for designating the course during navigation. In one such method the course is displayed on a CRT screen while being superposed on a map displayed on the same screen. In another, numerals or graph indicating a distance to an intersection at which the driver should turn the vehicle and pictures showing features of the intersection are displayed as information on this intersection. In a further method, a voice output is utilized as auxiliary means.
Conventional navigation apparatus, however, are designed to set a course from a starting point to a destination point and guide the driver along the course thereby set. If the driver fails to keep the vehicle on the desired course by making an error in identifying an intersection, he cannot continue traveling in accordance with the guidance effected by the navigation apparatus, unless he returns the vehicle to the course previously set or sets a new course by inputting the present position as a starting point. In this event, it is very troublesome for the driver to return to the course previously set as well as to set the present position as a starting point to determine a new course. That is, needless to say, the driver is unfamiliar with road circumstances of the particular region in which he is lost and, for this reason, he needs guidance. It is therefore difficult for him even to know his present position, although he knows the starting and destination points.
Whether or not the vehicle has passed over the desired intersection by traveling along the guidance course is determined by the distance through which the vehicle has traveled and the turning of the vehicle to the left or right which are detected by a distance sensor and a steering sensor. In practice, there is a problem of accumulation of errors in the detection which may cause an error in driver's decision. That is, since the distance through which the vehicle has traveled and turning to he left and right are detected on the basis of the setting of a course from the starting point to the destination point, distance errors are accumulated to an extent such that they cannot be corrected.